Department of Soil Technology xciii 



entails a decreased profit at some point in an increasing quantity of 

 fertilizer. For grain crops this point is reached with comparatively small 

 quantities of fertilizer. This experiment indicates that for hay the 

 profitable use of fertilizers may be extended to a considerably greater 

 quantity. 



The influence of the application of calcium in certain different chemical 

 combinations, and of ground limestone in different degrees of pulveriza- 

 tion, on the productiveness of certain loam and clay soils. — The experi- 

 ment involves the use of burned lime and ground limestone, and of lime- 

 stone ground to different degrees of fineness. The use of ground 

 dolomitic limestone containing about the same proportions of calcium and 

 magnesium, and of magnesium carbonate alone, is also being tried. The 

 soil on which the experiment is being conducted contains, in its native 

 state, a higher content of magnesium than of calcium. It furnishes, 

 therefore, a good medium for a test of the extent to which magnesium 

 carbonate may be used without injury. In selecting crops to be grown 

 in the experiment, legumes and sod crops are avoided and all pre- 

 caution is taken to use only crops that will not leave fertilizing residues 

 in the soil, the influence of which on succeeding crops would be increased 

 or decreased by the efifect of the lime. Secondary effects in experiments 

 of this kind must be avoided if primary causes are to be studied. 



Top-dressing alfalfa zvith farm manure and zvith different fertilisers, 

 also zvith lime. — The experiment is designed to ascertain whether alfalfa 

 may be profitably top-dressed with the materials named, especially after it 

 has been seeded for a number of years and is beginning to decrease in 

 hay production, or whether it is more profitable to plow it up and reseed. 

 The alfalfa now under experimentation was seeded in 1905. A very 

 profitable result has been obtained from the use of 100 pounds of super- 

 phosphate per acre. 



Continuous cropping of land zvith maize and hay; the latter crop being 

 designed to maintain the supply of organic matter in the soil, but omitting 

 entirely a return of mineral matter to compensate for that annually re- 

 moved by the crop. — Numerous experiments have demonstrated that 

 continuous cropping of soil without manures decreases crop yields, but 

 in such experiments the supply of organic matter has not been maintained. 

 In this experiment it is being attempted to keep up the supply of organic 

 matter by growing a hay crop four years and a maize crop one year in 

 every five. The hay is removed each year, but the sod is plowed under 

 when the land is prepared for maize. The yields of both hay and maize, 

 but especially those of maize, are being taken as a measure of the pro- 

 ductiveness of the soil. 



